Method for improving the quality of dealkylated aromatic compounds



March 21 1967 NELSON ETAL METHOD FOR 'IMPROVING THE QUALITY OFDEALKYLATED AROMATIC COMPOUNDS Filed June 23, 1965 ELWOCJD E. NELSON,RODNEY E. PETERSON e ELDON M. SUTPHIN United States Patent OificePatented Mar. 21, 1987 3,310,593 METHOD FOR IMPROVING THE QUALITY OFDEALKYLATED AROMATIC COMPOUNDS Elwood E. Nelson, Gihsonia, Rodney E.Peterson, Oakmont, and Eldon M. Sutphin, Pittsburgh, Pa., assiguors toGulf Research & Development Company, Pittsburgh, Pa., a corporation ofDelaware Filed June 23, 1965, Ser; No. 466,255

7 Claims. (Cl. 260672) This invention relates to a method for theproduction of hyperpure dealkylated aromatic compounds frompetroleum-derived dealkylated aromatic compounds and more particularly,it relates to a method for producing benzene which substantially exceedsstandard commercial specifications.

At one time a rather static benzene market was largely supplied withbenzene obtained as a by-product of the well developed but stabilizedcoal carbonization industry. Recovery of benzene from crude petroleum.in which it usually occurs as a very minor constituent was not asignificant factor. However, in recent years the rapid growth in thesynthesis of upgraded chemicals from benzene, such as synthetic rubbers,plastics, detergents and fine chemicals, has caused -a rapidlyincreasing and fluctuating demand for benzene which could not besupplied by the coal carbonization industry. I Fortuitously, benzene haslately been produced in relatively large amounts as a by-product in thepetroleum naphtha reforming process concurrently with this increasingdemand. Various alkyl aromatics such as toluene and the xylenes, whichare also produced in the naphtha reforming process, can be dealkylatedas a further source of benzene. In this expanding market cycles of overcapacity and under capacity have been a natural occurrence. These cyclesare expected to continue into the future as the result of future growthand adjustments to changing economic conditions.

Concomitant with this increase in. benzene usage is a demand by manyusers, sometimes without regard to process requirements, for benzenewhich surpasses the standards of established commercial specifications.In view of this fluctuating and highly competitive market for benzene,it would be most advantageous for a benzene supplier to be able toprovide material of a quality that would exceed the most rigidspecifications at no greater cost than lower specification material.Thus, not only could he fulfill every users requirements, but in periodsof over capacity he could easily sell his entire output, since users,with cost being equal, will buy the highest specification materialwhether or not it is required in their process. In the long run thiswould lead to a general upgrading of benzene and with the readyavailability of a purer material should lead to new usages. Inaccordance with our invention a hyperpure benzene is produced from thealkyl aromatic by-products of the naphtha reforming process at nogreater cost than less pure commercial grades of benzene.

In reforming petroleum hydrocarbons a naphtha fraction is firstsubjected to a hydro-genation-purification step to eliminate poisons tothe usually used. platinum reforming catalyst. In the subsequentreforming step, conducted in the presence of an excess of hydrogen undersuitable conditions of temperature and pressure, naphthenic constituentsare converted to aromatics, primarily benzene, toluene, xylene and ethylbenzene. These aromatics are separated from the reformate by solventextraction and may be distilled into exceedingly pure fractions.

Benzene is classified into a number of grades generally indicative ofits purity. Nitration-grade benzene carries the most rigid standardcommercial specification as set forth in ASTM D83S50. Under thisspecification its acid wash color, the most sensitive and significanttest, must not be greater than No. 2 on the acid wash color scale asdetermined by ASTM D848-62. In this test a benzene sample is agitatedwith 96 percent sulfuric acid and the resulting color of the acid layeris compared with a set of color standards numbered from 0 through 14with 0 being the color of distilled water.

With strict adherence to the proper processing conditions, it has beenpossible heretofore to make nitrationgrade benzene by the demethylationof toluene without any further treatment after the demethylation otherthan the customary separative procedures. If this demethylated productdoes not meet the specifications for nitrationgrade benzene, treatmentwith clay can bring the acid wash color down to No. 2, however, theattainment of a significantly lower number is not practically attainableby clay treatment since the clay quickly loses its effective ness andmust be frequently replaced at a prohibitive expense. Analysis of theuntreated demethylation efiluent by chromatographic and massspectroscopic analysis for color producing bodies or impurities hasfailed to identify any such substances. Notwithstanding this, we havemade the surprising discovery that by an appropriate modification of theprocess, the resultant product will far exceed the rigid specificationsfor nitration-grade benzene. Our invention is in part predicated uponthis discovery.

In our process an alkyl aromatic stream such as a stream of toluene fromthe reformate separation is subjected to an integrated dual treatment,first hydrogenatiug with an excess of hydrogen under appropriateconditions to demethylate the toluene and second treating in thepresence of this hydrogen under different conditions to ensure that theproduct will exceed the most rigid commercial specifications. Accordingto our process benzene 1 can be produced with an acid wash color as lowat 0+,

which is almost water white under the test. We accom: plish this byimmediately subjecting the demethylation effiuent to an elevatedtemperature and pressure in the presence of hydrogen and a solidparticulate material.

We do not know what direct effect that this has on the effiuent otherthan the discovery that the benzene product obtained after the finaldistillation far exceeds the specifications for nitration-grade benzene.Knowing that at least three separate purifying-hydrogenation operationsas Well as the associated purifying-separative procedures are involvedfrom the original refinery distillationthrough this demethylation, it iswholly unexpected and highly surprising that a further treatment of thisessentially pure demethylated product under these conditions wouldproduce a strikingly superior-specification material.

The bromine index of benzene is frequently used in commercial dealingsin substitution of or to supplement the acid wash color test although itis not a part of the official specifications In typical examples theeffluent from the toluene demethylator exhibited a bromine index ofabout 20 as determined by ASTM D1491-60. This without further treatmentis superior by several orders of magnitude to material produced by priorprocesses even after special treatment. For example, in U.S. Patent No.2,701,267, crude benzene obtained by the steam distillation of wash oilused in the recovery of light oil from coal distillation gases isprepurified and then is subjected to a catalytic treatment with a largequantity of hydrogen at elevated temperature and pressure. This gives afinal benzene, stated to be pure, having a bromine number of 0.2 whichcorresponds approximately to a bromine index of 200. It is thereforehighly unexpected that the bromine index of the demethylation efiluent,which is lower by a factor of about 10 than the pure benzene resultingafter final treatment under this patent, can be substantially reduced byour treatment. Despite this, we have made the surprising discovery that,if the demethylation efiluent is subjected to suitable conditions oftemperature and pressure in the presence of a solid particulatematerial, a benzene having a bromine index less than and in manyinstances under 1.0 is produced.

The drawing illustrates an arrangement for carrying out our invention.Toluene 1 from the naphtha reformate separation admixed with recycletoluene 12 is introduced into the system and hyperpure benzene 2 isobtained as the primary product. The toluene is first mixed with anexcess of hydrogen 3 and the mixture heated prior to introduction intothe demethylation unit 4. After demethylation, the benzene-rich effluentis treated in upgrading unit 7 to reduce the acid wash color and bromineindex of the final benzene product to an extremely low value. Aftergas-liquid separation in 8 and final removal of gases and light ends instripper 9, the liquid effluent is separated in fractionator 10 intohyperpure benzene 2 as the major product as well as a more volatilefraction 11, unreacted toluene 12 suitable for recycling, and lessvolatile byproducts 13. This less volatile bottoms product can befurther separated into one or more of its components in a hyperpurestate, if desired, including naphthalene, biphenyl, fluorene,phenanthrene, and pyrene, or this fraction may be fed into the refineryfuel oil stream.

In more specific detail the toluene-hydrogen feed is sequentially heatedin heat exchangers 15 and 16 by the effluent stream from the upgradingunit 7 and by the demethylator efiluent stream 17 and in furnace 18fired with refinery fuel gases 14 to bring the mixture to reactiontemperature for thermal demethylation. This reaction occurs betweenabout 1150 and 1800 F. with l250 to 1350 F. being the preferred rangeand about 100 to 1000 p.s.i.g., preferably in the range of 400 to 600p.s.i.g. An excess of 1.5 to 20 mols of hydrogen per mol of hydrocarbonis generally used with the preferred molar ratio being 3 to 8 mols ofhydrogen per mol of hydrocarbon. The mixture is retained in reactor 4for sufficient time, from one to 600 seconds and preferably from 10 to100 seconds, to obtain the desired demethylation. This procedure asdescribed merely represents a preferred mode of operation. Demethylationmay also be performed hereunder in a catalytic reaction using a suitabledealkylation catalyst at a temperature somewhat lower, such as 1000 to1400 F than is used in the non-catalytic reaction.

Heat economy is effected by utilizing the hot eflluent 17 from thedemethylator to sequentially heat the feed in heat exchanger 16, to heatthe fractionator bottoms in heat exchanger 20, and to drive thestripping column in heat exchanger 21 prior to its introduction intotreating unit 7. This upgrading operation is broadly carried out atabout 150 to 600 F., at 100 to 1000 p.s.i.g., and at a liquid hourlyspace velocity at 1 to 20 volumes of liquid per hour per volume of solidparticulate material. Preferred conditions for operation are about 200to about 550 F., about 300 to about 500 p.s.i.g., and a liquid hourlyspace velocity of l to 8. Suitable solid particulate materials for usein the upgrading unit include the metals, metal oxides and sulfidedmetals of Group VI (left column) and Group VIII of the Periodic Tablealone or in admixture, distended on non-acidic supports. These includenickel-cobalt-molybdenum, cobalt molybdenum, sulfided nickel, sulfidedtungsten-nickel, sulfided tungsten on such non-acidic carriers asalumina, clay, and kieselguhr and the like. Primary process control iseffected by varying the liquid hourly space velocity.

The effluent stream from treating unit 7 passes through heat exchanger15 which provides the initial heating to the toluene-hydrogen feedstream and through cooler 22 into gas-liquids separator 8 for separationof the gases, primarily hydrogen and methane, from the liquid portion ofthe cooled stream. Residual gases and light hydrocarbons are removed instripper 9 and the liquid bottoms product 23 is fractionated into superspecification benzene 2 and the other previously described fractions.

Gas-vapor streams 24 and 25 from the gas-liquids separator and thestripper are introduced into the vapor recovery unit 26 from which asmall amount of separated liquids 27 is passed to the fractionator. fromthe vapor recovery unit are recycled through compressor 31 afterbleeding off a small slip stream 32 to maintain the hydrogen content ofthe feed stream at an appropriate level. Makeup hydrogen 33 from thereformer off-gases or other available source is added to the recycle gasstream.

The following is a specific example of the operation of the invention inwhich hyperpure benzene is produced from toluene. Fifteen thousandlbs/hr. toluene from .'the reformate extraction which includes arelatively small proportion of recycle toluene from the fractionator iscombined with a mixed stream of reformer off-gas and recycle hydrogenhaving a net hydrogen content of about 75 mol percent to form a hydrogento toluene mol ratio of 3.5 to 1. This mixture is preheated to about1l70 to 1250 F. and charged to the demethylator operating at a pressureof about 460 p.s.i.g. Two reactors in series are used with coolingbetween stages to maintain the desired temperature of reaction. After atotal contact time of about 40 seconds, the demethylated efiluent isquenched by heat exchange with the input stream. After cooling theeffluent stream by heat exchange in the fractionator and in the stripperreboiler as described, it is fed to the treating unit at a temperatureand pressure of 450 F. and 350 p.s.i.g. and a flow rate of four liquidvolumes per hour per volume of solid particulate material. The solidparticulate material in the treating unit is a presulfided mixturecontaining 2.3 percent nickel, 1.4 percent cobalt, and 9.2 percentmolybdenum supported on alumina. After separation from the gases, theliquid effluent from the treating unit is fractionated to produce 10,700pounds of hyperpurse benzene per hour. The following is an actualanalysis which is representative of this operation:

l Treating unit by-passed.

2 Treating unit in operation. It is of particular interest to note thatthe improvement in acid wash color does not show up until afterfractionation While the improvement in bromine index does not appear tobe significantly improved by fractionation. Of further significance arethe excellent results obtained after long usage of the solid particulatematerial. In many runs over the range of preferred conditions ofoperation the benzene product consistently displayed an acid wash colorof 1- or better and a bromine index under 5, indicating a good toleranceto reasonable variations in operation. Furthermore, both the selectivityof toluene to benzene and the per-pass conversion efiiciency ex- Thegases 30 ceeded 90 percent in these runs. This high degree ofselectivity and conversion efliciency can be consistently obtained withproper operation within the preferred conditions.

At the more rigorous conditions of operation some cyclohexane isproduced in the upgrading operation. For example, three runs werecarried out at a pressure of 400 p.s.i.g., a temperature of 550 F., anda total gas rate of 10,500 s.c.f./bbl. aromatics, the gas consisting of50 percent hydrogen and 50 percent methane. For liquid hourly spacevelocities of 2, 3 and 4 the cyclohexane product amounted to .035, .025and .015 volume percent respectively. In order to decrease the amount ofcyclohexane, the temperature or pressure may be reduced or the liquidhourly space volicty may be increased, or more than one of thesevariables may be mutually adjusted in the appropriate direction.

It is of critical importance to the successful economical utilization ofour process that it be integrated into an energy conserving system asdescribed. Although toluene was specifically described as the feedmaterial, other petroleum-derived materials are also suitable includingxylene, ethyl benzene and other monoalkyl and polyalkyl benzenecompounds alone or in admixture with toluene. These aromatic compoundsare also converted to hyperspecification benzene at high conversionefiiciency and good selectivity. In addition, this process can be usedto produce hyperpure dealkylated polynuclear aromatic compounds, such asnaphthalene, from the corresponding alkylated polynuclear compounds.

It is to be understood that the above disclosure is by Way of specificexample and that numerous modifications and variations are available tothose of ordinary skill in the art without departing from the truespirit and scope of our invention.

We claim:

1. A process for the production of hyperpure dealkylated aromaticcompounds which comprises heating a composition selected fromthe groupconsisting of an alkyl aromatic compound and a mixture of alkyl aromaticcompounds and about a 1.5 to 20 molar excess of hydrogen to atemperature and pressure between about 100 0 to 1800 F. and 100 to 1000p.s.i.g. for about one to 600 seconds; subjecting the effluent mixturewhich is substantially free of organic sulfur compounds to a temperatureand pressure between about 150 to 600 F. and 100 to 1000 p.s.i.g. in thepresence of a solid particulate material selected from the groupconsisting of metals, metal oxides and sulfided metals of Group VI (leftcolumn) and VIII of the Periodic Table, and mixtures thereof, distendedon a non-acidic suport; and separating the treating efiluent mixtureinto fractions of hyperpure dealkylated aromatic compounds.

2. A process for the production of hyperpure dealkylated aromaticcompounds which comprises heating a composition selected from the groupconsisting of an alkyl aromatic compound and a mixture of alkyl aromaticcompounds and about a 1.5 to 20 molar excess of hydrogen to atemperature and pressure between about 1000 to 1800 F. and 300 to 1000p.s.i.g. for about one to 600 seconds; subjecting the efiluentmixturewhich is substantially free of organic sulfur compounds to atemperature and pressure between about 200 to 550 F. and 300 to 500p.s.i.g. in the presence of a solid particulate material selected fromthe group consisting of metals, metal oxides and sulfided metals ofGroup VI (left column) and VIII of the Periodic Table and mixturesthereof, distended on a non-acidic support, at the rate of about 1:1 to8:1 liquid volumes of effluent mixture per hour per volume of solidparticulate material, and separating the treated eflluent mixture intofractions of hyperpure dealkylated aromatic compounds.

3. A process for the production ofhyperpure benzene which comprisesheating a composition selected from the group consisting of an alkylaromatic compound and a mixture of alkyl aromatic compounds and about a1.5 to 20 molar excess of hydrogen to a temperature and pressure betweenabout 1000 to 1800 F. and 100 to 100 p.s.i.g. for about one to 600seconds; subjecting the efliuent mixture which is substantially free oforganic sulfur compounds to a temperature and pressure between about 150to 600 F. and 100 to 1000 p.s.i.g. in the presence of a solidparticulate material selected from the group consisting of metals, metaloxides and sulfided metals of Group VI (left column) and VIII of thePeriodic Table, and mixtures thereof, distended on a nonacidic support;and separating hyperpure benzene from the treated eflluent mixture.

4. A process for the production of hyperpure benzene which comprisesheating a composition selected from the group consisting of an alkylaromatic compound and a mixture of alkyl aromatic compounds and about a1.5 to 20 molar excess of hydrogen to a temperature and pressure betweenabout 1000 to 1800 F. and 300 to 1000 p.s.i.g. for about one to 600seconds; subjecting the effiuent mixture which is substantially free oforganic sulfur compounds to a temperature and pressure between about 200to 550 F. and 300 to 500 p.s.i.g. in the presence of a solid particulatematerial selected from the group consisting of metals, metal oxides andsulfided metals of Group VI (left column) and VIII of the Periodic Tableand mixtures thereof, distended on a nonacidic support; and separatinghyperpure benzene from the treated effluent mixture.

5. A process for the production of hyperpure benzene which comprisesheating a mixture of toluene and about a 1.5 to 20 molar excess ofhydrogen to a temperature and pressure between about 1000 to 1800 F. and100 to 1000 p.s.i.g. for about one to 600 seconds; subjecting theeffluent mixture which is substantially free of organic sulfur compoundsat a temperature and pressure between about 150 to 600 F. and 100 to1000 p.s.i.g. to a catalytic material selected from the group consistingof metals, metal oxides and sulfided metals of Group VI (left column)and VIII of the Periodic Table, and mixtures thereof, distended on anon-acidic support; and separating hyperpure benzene from the treatedefiluent mixture.

6. A process for the production of benzene having an acid wash colorless than No. 2 which comprises heating a mixture of toluene. and abouta 1.5 to 20 molar excess of hydrogen to a temperature and pressurebetween about 1000 to 1800 F. and 100 to 1000 p.s.i.g. for about one to600 seconds; subjecting the eflluent mixture which is substantially freeof organic sulfur compounds to a temperature and pressure between about150 to 600 F. and to 1000 p.s.i.g. in the presence of a solidparticulate material selected from the group consisting of metals, metaloxides, and sulfided metals of Group VI (left column) and Group VIII ofthe Periodic Table, and mixtures thereof, distended on a non-acidicsupport at the rate of 1:1 to 20:1 liquid volumes of effluent mixtureper hour per volume of solid particulate material; and separatinghyper-specification benzene from the treated eflluent mixture.

7. A process for the production of benzene having an acid Wash colorless than No. 2 which comprises heating a mixture of toluene and about a3 to 8 molar excess of hydrogen to a temperature and pressure betweenabout 1100 to 1350 F. and 400 to 600 p.s.i.g. for about 10 to 100seconds; subjecting the effluent mixture which is substantially free oforganic sulfur compounds to a temperature and pressure between about 200to 550 F. and 300 to 500 p.s.i.g. in the presence of a solid particulatematerial selected from the group consisting of metals, metal oxides andsulfided metals of Group VI (left column) and VIII of the PeriodicTable, and mixtures thereof, distended on a non-acidic support at therate of 1:1 to 8:1 liquid volumes of effluent mixture per hour pervolume of solid particulate materials; and separatinghyper-specification bznzene from the treated effiu- 3,150,196 9/ 1964Mas6 11 2 60-672 ent mixture. 3,213,150 10/1965 Cabbage 260672References Cited by the Examiner 3,222,410 12/1965 SWHHSQD UNITED STATESPATENTS 5 DELBERT E. GANTZ, Primary Examiner.

2,876,268 3/ 1959 Ciapefifl et G. E. SCHMITKONS, Assistant Examiner.

2,957,925 10/1960 Oettinger 260-674

1. A PROCESS FOR THE PRODUCTION OF HYPERPURE DEALKYLATED AROMATICCOMPOUNDS WHICH COMPRISES HEATING A COMPOSITION SELECTED FROM THE GROUPCONSISTING OF AN ALKYL AROMATIC COMPOUND AND A MIXTURE OF ALKYL AROMATICCOMPOUNDS AND ABOUT A 1.5 TO 20 MOLAR EXCESS OF HYDROGEN TO ATEMPERATURE AND PRESSURE BETWEEN ABOUT 1000* TO 1800*F. AND 100 TO 1000P.S.I.G. FOR ABOUT ONE TO 600 SECONDS; SUBJECTING THE EFFLUENT MIXTUREWHICH IS SUBSTANTIALLY FREE OF ORGANIC SULFUR COMPOUNDS TO A TEMPERATUREAND PRESSURE BETWEEN ABOUT 150* TO 600*F. AND 100 TO 1000 P.S.I.G. INTHE PRESENCE OF A SOLID PARTICULATE MATERIAL SELECTED FROM THE GROUPCONSITING OF METALS, METAL OXIDES AND SULFIDED METALS OF GROUP VI (LEFTCOLUMN) AND VIII OF THE PERIODIC TABLE, AND MIXTURE THEREOF, DISTENDEDON A NON-ACIDIC SUPORT; AND SEPARATING THE TREATING EFFLUENT MIXTUREINTO FRACTIONS OF HYPERPURE DEALKYLATED AROMATIC COMPOUNDS.